I recently came across a number of SPARCstation 20 boxes and decided to restore a few of them to a "new" condition. I am quite impressed with the overall design and build quality of the units. However, when cleaning and inspecting the power supplies I discovered that some of the output filter capacitors began to vent electrolyte (not surprisingly). The power supplies were still functioning correctly and the ripple was within reasonable range, but I expect that the deterioration would rapidly accelerate under use.

I have now rebuilt the power supplies and replaced all of the aluminum electrolytic capacitors with high quality long life components. This reduced the output voltage ripple and will hopefully allow the supplies to carry on for another 20 years. If anyone is interested, I would be more than happy to post the replacement parts list.

I'll have to put "inspect SS20 PSU" near the top of my "to do" list. Now that I know about the potential for trouble lurking in there, I'd certainly prefer to fix the PSU before any serious problems crop up or any damage is done.

I am attaching a PDF with a DigiKey parts list and with the original component details for the FDK PEX668-31 power supplies that my SPARCstations were equipped with. Note that some of the capacitors are installed on daughter boards and are either very difficult or impossible to rework without removing the daughter boards. The parts most likely to fail are C32, C35 and C27, C29 on the output filter side, but I replaced all of the capacitors on my power supplies, including the input side (line) filter.

Please be careful when working with the power supply as the input capacitor stores enough energy to be lethal - check its voltage to confirm that it is fully discharged before handling.

Well, I inspected my SS20's PSU last night. Fortunately there are no signs of leaking electrolytes...yet. Which is a good thing, because looking at it suggests that re-capping it is going to be beyond my (current) soldering skill level. Those daughter boards are going to be tricky to work with for sure. Here's hoping mine keeps working until I get more comfortable with soldering circuit boards! (I'm definitely a software guy.)

Again, thanks for the warning. I wouldn't have thought to inspect my PSU without it. And even bigger thanks for the very detailed replacement parts list. It looks like a lot of work must have gone into finding suitable replacements for all those capacitors. It will make it a lot easier for the rest of us to fix ours when (not if!) the time comes.

wikipedia wrote:As an electrolytic capacitor ages, its capacitance usually decreases and its equivalent series resistance (ESR) usually increases. The capacitance may abnormally degrade to as low as 4% of the original value, as opposed to an expected 50% capacity degradation over the normal life span of the component. When this happens, the capacitors no longer adequately serve their purpose of filtering the direct current voltages on the motherboard, and a result of this failure is an increase in the ripple voltage that the capacitor is supposed to filter out. This results in a system instability. Capacitors with high ESR and low capacitance can make power supplies malfunction, sometimes causing further circuit damage. In computers, CPU core voltage or other system voltages may fluctuate or go out of range, possibly with an increase in CPU temperature as the core voltage rises.

Project:Temporarily lost at sea...Plan:World domination! Or something...

wikipedia wrote:As an electrolytic capacitor ages, its capacitance usually decreases and its equivalent series resistance (ESR) usually increases. The capacitance may abnormally degrade to as low as 4% of the original value, as opposed to an expected 50% capacity degradation over the normal life span of the component. When this happens, the capacitors no longer adequately serve their purpose of filtering the direct current voltages on the motherboard, and a result of this failure is an increase in the ripple voltage that the capacitor is supposed to filter out. This results in a system instability. Capacitors with high ESR and low capacitance can make power supplies malfunction, sometimes causing further circuit damage. In computers, CPU core voltage or other system voltages may fluctuate or go out of range, possibly with an increase in CPU temperature as the core voltage rises.

Thanks for the info guys... must check my SPARCstations for this capacitor problem.

Indeed, and I had to do that for my "primary" machine. However, if the installed NVRAM is original and still carries the orange barcode sticker, the NVRAM content can be recreated from the sticker. A complete guide to reprogramming the NVRAM can be found at:

The SPARCstation 20 uses an STM M48T18-150 Timekeeper NVRAM with built-in battery. An exact replacement can be obtained from DigiKey under their part number 497-2838-5-ND. Note that the mechanical envelope has been changed slightly by STM and this new part will no longer fit into the plastic chip carrier / frame that the SPARCstation 20 uses to ease the chip removal. But it fits perfectly into the socket and functions perfectly as well.

Hi,I know it is an old thread but after a full capacitor-replacement of the SS-20 Power Supply, the computer does not turn on anymore (not even the fans). Actually it is completely dead. We have used the same values of capacitors (some capacitors with higher voltage value).

A second SS-20 we have here is working (with it's old capacitors), so we have double-checked that the lines are not corrupted and fuse is also ok. Before the capacitors replacement, SS-20 was turning on but we had to do this because of capacitors leakage. Power switch seems good, the computer also does not turn on via keyboard.

Have you used the capacitor models and part numbers from my list or just "any" capacitors of same capacity and voltage rating?

In switching power supplies it is critical to use the correct low impedance capacitors in order for them to function correctly. When I put the replacement list together I matched the new capacitors to the specifications to the originals, ensuring that they are at least as good in terms of impedance. In general I pick the absolute best quality long-life parts for the recap jobs to make sure that they survive for a very long time. Note, however, that too low impedance is also not good as it may cause power supply instabilities.

Are you sure that nothing got damaged during your recap and that you soldered and assembled the power supply correctly?

We have used high quality capacitors of same capacity and voltage rating (some capacitors have higher voltage value). The work of recapping has been done professionally and lines have been checked for errors, wrong joints or short circuits, according to the other power supply which is working. As the power supply is completely dead, I suspect another component that died during the first turn-on (probably due to the current correct voltage of the new capacitors).

All switch-mode power supplies use similar fundamental topologies, but detailed implementations vary. The best thing I would suggest is contacting Fuji in an attempt to obtain the power supply schematic. It is a long shot, but being persistent helps and I was able to do this successfully for other power supplies in the past...

Beyond this, a good electronics repair shop would be able to troubleshoot and repair the unit, but this approach would be rather expensive. It would be cheaper to purchase a replacement power supply.